The Apimonitor (Acoustic Hive Monitor)

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1 The Apimonitor (Acoustic Hive Monitor) Version 1.0. Copyright Notice: Copyright P Zimmermann This document may be copied, printed and freely distributed on condition that no changes are made to the text and no charge is made either for distribution or reproduction. Reproductions of this document must be accompanied by acknowledgement of the source of the original data. Copyright P. Zimmermann 2010 Page 1

2 CONTENTS 1 Introduction 2 Design Philosophy 3 Outline definition 4 The Electronics - A Bit More Detail 5 Operating Instructions 6 Maintenance / Testing 7 Notes For The Experimenter 8 Appendix Copyright Notice: Copyright P Zimmermann This document may be copied, printed and freely distributed on condition that no changes are made to the text and no charge is made either for distribution or reproduction. Reproductions of this document must be accompanied by acknowledgement of the source of the original data. Copyright P. Zimmermann 2010 Page 2

3 1.0. Introduction; The Apimonitor has been developed in response to an apparent demand for an up to date and reproducible means of determining activity within the bee colony, specifically the precursory activity to swarming. The link between acoustic activity and colony swarming has been known for a number of years and a great deal of work was carried out by the late Eddie Woods, who not only proved the link but made many measurements of the frequencies produced, and by carrying out these measurements on active hives was able to demonstrate the correlation between the two. The measurement data was predictable enough for Eddie to produce his own device which he called the Apidictor. This device used early transistor technology and was produced in small numbers in the early 60 s. A more detailed description of Eddie s work can be found at the following website It must be emphasized that the Apimonitor described within this document is not a copy of the original Apidictor, it is instead a measurement device, that will allow a beekeeper to monitor the sounds within the hive and with practice to be able to predict the onset of swarming. To this end, the Apimonitor has been developed with filters of similar frequencies to those used in the original Apidictor. However, due to the differences in component technologies and the lack of hard data regarding the performance of the original Apidictor, the performance of the Apimonitor will invariably be different and the need for practice along with detailed hive observation will still be paramount for successful operation. I make no claims as to the originality of any of the circuitry published here. So, look upon the Apimonitor as a tool to listen with and to assist with making judgements based on your own observations of hive activity and bee behaviour. The Apimonitor may well work sufficiently well to be of use in the intended manner, however, I suspect that it will benefit from additional testing which will need to be carried out along with observations of bee activity, which may in the long term lead to better / different filter characteristics and gains. As such, the design presented within this document should be viewed as a starting point and will not give a yes / no answer to the questions Are my bees about to swarm? or Has my queen gone AWOL? As I do not have the time and facilities to do in depth testing and measuring in the field as it were, I am presenting this design as an open source design, into the public domain. You are welcome and indeed encouraged to copy it / modify it as you see fit with the proviso that all information, drawings etc are copied along with appropriate acknowledgements of the source of the original data. I would very much welcome feedback from any one who has a chance to try out this design along with any modifications or changes that may result. Copyright P. Zimmermann 2010 Page 3

4 2.0. The Design Philosophy: The design presented here was conceived as a result of an apparent need for an up to date acoustic hive monitor. However, before proceeding with the design, there were several ground rules, which had to be established first. These helped to keep track of the original requirement and are listed below in no particular order: Keep things as simple as possible Keep it as cost effective as possible We are not trying to re-invent the wheel here so we won t try stick to well proven principles and technology As well as being able to listen to the sounds within the hive, a basic relative measure of sound level would be highly desirable We will be using a microphone to measure airborne sounds within the hive. It is not the intention to measure sound vibration through contact with the hive structure; although this may be an alternative approach should someone else choose to pursue it. The measuring microphone is to be small, rugged and cheap for ease of replacement. The environment within the hive is not a benign one and the microphone may well get damaged or propolised! 2.6. The complete unit is to be portable and battery powered Means shall be provided to enable connection of a secondary monitor / recording device Avoid exotic components, industry standard components are to be used wherever possible. This will make DIY build, component sourcing and repair much easier. This set of ground rules although not exhaustive, already eliminates certain options and defines the bones of our design. In addition, with particular reference to 2.3. above, we already know the following about Eddie Woods Apidictor:- There were 3 switch settings: Switch position 1 provided an All Pass function with no filtering. Switch position 2 provided a Band Pass function to listen to the warble. Switch position 3 was a High Pass function to listen to the hiss. An indicator was provided for the measurement of relative level. Copyright P. Zimmermann 2010 Page 4

5 To add a bit more detail to some of these original functions, a brief description of each as I understand them follows: The All Pass function is basically an amplifier with a flat response. There is no deliberate attempt to apply filtering to the microphone signal, so what the microphone picks up is what we hear. (Subject to the limitations of the microphone and the vagaries of the human ear of course!) The Band Pass function allows a predefined narrow range of frequencies through to the indicator and headphones. Frequencies above and below this narrow band are progressively attenuated (reduced). Various sources state that the original Apidictor band pass filter had a pass band of 225 to 285Hz and as we have no reason to change it, we will stick with something similar. The function of the Band pass filter is to isolate the warbling sound that the bees make from general background noise and thus make it more readily audible and therefore measureable. What is debatable though is the sharpness or selectivity of the filter. I have seen several different sources of graphs purporting to be measurements of the Apidictor filter response, but no firm evidence to support this. Unfortunately, the filter response has a direct effect on any measurements made so the selectivity or Q of the filter is fundamental to the unit performance. For the moment we will adhere to the time honoured method of the first order guesstimate. Most analogue filters are inevitably compromises and this one will be no different. The filter ultimately will be a balance of effectiveness, simplicity, stability and cost whilst at the same time adhering to the original frequency requirements as much as possible. The High Pass function is basically an amplifier that allows more of a signal to pass as the frequency increases. Thus it provides a rising response where the amplitude (loudness) of the signal rises as the frequency or pitch of the signal increases. The function of the High Pass filter is to enable us to listen to the high pitched hiss that bees make under certain conditions. The original Apidictor had a filter with a 3kHz corner frequency, which we will also retain for our own design. Don t worry too much about the filter terminology here, more detailed explanations will follow later. Finally the last key item was an indicator. The Apidictor used a magic eye, which was in common use at the time. It was a special variant of the vacuum valve but is now outdated technology and not suitable for a portable, low power approach. We will retain an indicator but it will operate in a slightly different manner and will be more suitable for a low cost portable item. Copyright P. Zimmermann 2010 Page 5

6 3.0. Outline Definition: We now have some limited visibility of our basic design and can now identify the main functional blocks that need our attention. Microphone Microphone Amplifier All Pass Filter Level Detector Indicator Band Pass Filter Selector Switch Headphone Amplifier Headphones High Pass Filter Fig. 1 Block Diagram Line Level Output Output to Recorder Microphone: Small, rugged and cheap pretty much defines the modern electret microphone. They are to be found in all sorts of equipment from portable stereos, karaoke machines, car alarms to telephones. They are available as noise cancelling types which will reject a certain amount of background noise but in this application I don t think that will be an overriding requirement. In contrast to a moving coil microphone, an electret microphone needs power to be able to function. Most common or garden electrets will work with any supply voltage in the range of 1.5 volts to 10 volts Ideal for our battery powered unit. Indicator: Moving coil meters are relatively expensive items these days and if you are gutting an old piece of equipment then it may well be suitable with a bit of tweaking of the circuit. However, I am going to assume that anyone intending to buy or build one of these units will be keeping a careful eye on the costs and so the meter will not be included in this design. What we will use however is a LED (light emitting diode). These are extremely common cheap and rugged and by combining with a judicious bit of circuitry can be made to suit our purpose here quite well. Headphones: Again in order to keep the costs down, I am assuming that most people will have access to a cheap pair of MP3 type stereo headphones. These are normally of 32 ohm impedance (sometimes higher) and we will use them in mono mode. Higher impedance headphones, if you have them will probably be ok, but if you have low impedance (<32 ohm) headphones, I m afraid they won t be suitable for use with this unit. Copyright P. Zimmermann 2010 Page 6

7 Recorder Output: As previously mentioned, a facility to be able to connect an external recording device is to be included. This could be a cassette recorder, solid state recorder or a computer sound card. The output level will be appropriate for any of these that utilize a line input. This feature will enable recorded sounds to be analysed at leisure away from the hive. From the preceding list of requirements a design was commenced culminating in the schematic shown in the appendix. The schematic is presented here for those of you who are interested or want to modify the unit to suit your own particular needs. If you don t understand electronics or are just not interested then skip the next section and concentrate on the operating instructions. Copyright P. Zimmermann 2010 Page 7

8 4.0. The Electronics - A Bit More Detail: This section describes each section of the Apimonitor design in a bit more detail for those of you who are either interested or want to take things a bit further and carry out modifications / changes of your own. The complete schematic can be found in the appendix and the following sections will detail the operation of the various functional blocks. Skip to section 5.0. if electronics doesn t interest you Microphone: This is a rather fundamental part of the Apimonitor. It is a key item and the successful performance or otherwise of the Apimonitor will be directly proportional to the performance of the microphone. Rubbish in = Rubbish out! Care should be taken if you intend using an alternative type. The microphone selected for use in this application is a fairly typical, small and rugged electret microphone. The data sheet for the chosen microphone can be found in the appendix. Its main features that are useful here are: i. Low cost ii. Relatively easy to obtain. iii Physically small - it can be placed inside the hive relatively easily, but not so small that we can t handle and solder it easily. iv. A flat frequency response and good sensitivity. The frequency response is fairly flat over the range of frequencies that we are interested in (approx 50Hz to 10kHz) and it is sensitive enough that we don t need too much amplification. The sensitivity of the microphone is specified in dbv, which is a logarithmic measure of output voltage and usually (but not always) specified at 1 Pascal at a known or specified distance from the sound source. The Pascal is a measure of pressure and is used to specify acoustic sound pressure level (SPL). There are many different types of microphone on the market that could be used but there are one or two things to bear in mind if you are thinking of trying a different one. Firstly, to operate correctly with this circuit it must be an electret type. This type of microphone generally has a small amplifier / buffer built into the microphone itself and thus generally has a high sensitivity and good frequency response. The downside however, is that it needs power to operate correctly. Modern day computers, phones and all sorts of electronic devices use electret microphones and it is possible to try any number of these for comparison. Just observe the correct polarity when connecting up connecting it up back to front probably won t damage it, but it won t work either. Do bear in mind though that a microphone of different sensitivity will give you different results with your Apimonitor. It may or may not be significant, depending on the difference in sensitivity and frequency response of your chosen microphone. Do not try to connect a moving coil type of microphone to this circuit. No damage will be caused but no or very little output will be heard. Moving coil microphones in general have too low an output to be used without resorting to an external pre-amplifier and will often have a frequency response that is far from flat. Copyright P. Zimmermann 2010 Page 8

9 4.2. Type of Amplifier: The amplifier used in this circuit is a well-known industry standard that has been around many years now, the TL064. It is a Low Power JFet input operational amplifier which in a nutshell means it is well suited to low power, battery operated applications such as this. The main features of the TL064 that we make use of are: i. Low power consumption typically 200uA per amplifier. ii. High Gain / Bandwidth. (1MHz) iii. 4 amplifiers in one package. iv. Relatively wide operating voltage range. v. Commonly available There are many other amplifiers that could be used in this application but as with all things, there are trade offs and compromises. The TL064 is rather unique in that it is specified to operate down to 6 volts and below. The TL074 / TL084 amplifiers are very similar in performance but they will draw more power and hence battery life will be shorter pro rata. Probably not a major issue but for long term monitoring it could be. The OPA 4705 series from Texas are another good range with very similar performance to the TL064. I could go on and on but there really are far too many options and manufacturers to list them all here. The choice is yours, but use the TL064 as your baseline for any comparisons. 4.3 The Microphone Amplifier: This stage is configured as a non-inverting, ac-coupled amplifier. It serves to match the microphone output to the rest of the circuitry and also to amplify the signal up to a useable level. The nominal mid-band gain is set to 28dB (x25). The microphone input is applied via capacitor C5 and resistors R6, R7 set the overall gain. Capacitor C5 also blocks any DC content in the input signal from reaching the amplifier input. Resistors R10, R19 are connected to the +9 volt supply and supply the bias voltage needed by the electret microphone in order for it to work correctly. Copyright P. Zimmermann 2010 Page 9

10 4.4 The High Pass Filter: The amplifier shown left is the second of four in the package U1. Its purpose is to take the amplified microphone signal from the microphone amplifier above and to apply a high pass function, which will attenuate lower frequencies whilst passing higher frequencies unchanged. The transition between the two is smooth and at a pre determined rate of 12 db per octave. This circuit configuration is known as a 2 pole filter and although it attenuates frequencies below its corner frequency, it does not amplify above its corner frequency. The corner frequency is set by C1, C2 and R2 and is nominally 3kHz The Band Pass Filter: Shown left is the band pass filter, the function of which is to pass a narrow pre-defined range of frequencies and attenuate frequencies outside this range. The band pass function is centered on approx. 255Hz and the sharpness or Q of the filter is controlled by the ratios of the components around U1C. Although these types of filters can be made adjustable, one of the drawbacks is that the adjustments for frequency, bandwidth and gain are interdependant. This stage does yield a small amount of gain of approx. 6dB (2x). No end of tweaking could be done to the band pass filter to optimize it for the frequencies of interest. However, this is a suggested starting point and modifications / changes are done at the discretion of the individual. Copyright P. Zimmermann 2010 Page 10

11 4.6. The All Pass Amplifier: As its name suggests, the all pass amplifier passes all frequencies within its pass band essentially unchanged. This circuit configuration, as well as inverting the signal can also supply gain if required. The gain is controlled by the ratio of resistors R8 and R9, which in this instance fix the gain at 0dB (or x1). 4.7 The Level Detector: The level detector compares the input from the level control (R13) with a fixed dc reference. If the input level exceeds the reference level the amplifier will amplify the difference and its output will move positive, lighting the LED. The greater the signal difference, the brighter the LED will light. This operates as a very simple measurement function for a fixed microphone position and sound level, the level control R13 is gradually increased (clock wise) until the LED is just lighting. The position of the level control knob against its background scale will then give a relative indication of signal level. Thus the louder the signal being monitored, the lower the position of the level control knob for the LED to light. Although somewhat crude this method avoids the use of a relatively costly and delicate meter and is fairly intuitive to use once familiar with its operation. See the operating instructions for more detail on this function. It should be noted that this form of level detector is supply dependant. i.e. As the battery voltage reduces, the sensitivity of the detector will change in proportion, but not so much as to cause a problem in use. Again, this limitation is part of the keep it simple compromise. Copyright P. Zimmermann 2010 Page 11

12 4.8 The Headphone Amplifier: The primary purpose of the headphone amplifier is to make the microphone output audible to the operator of the Apimonitor. It also serves to perform a check on the microphone to see that it is working correctly and is not subject to a broken cable or intermittent connection. The headphone amplifier shown above is slightly unusual in that op-amps aren t normally used to drive headphones, as they don t have enough power drive capability. However, as we are only using 32 Ohm or higher impedance headphones, we can cheat a bit. By paralleling three amplifiers, U2B, U2C and U2D their combined output is just sufficient for our purpose. This is not really recommended practice but for our application it works well enough and keeps the costs to a minimum. It should be noted that the headphone amplifier does not provide any voltage gain but does provide power gain. The headphone amplifier will drive 32 Ohm or higher MP3 type headphones but will not drive low impedance 8 Ohm types. If you require Hi Fi quality audio, then you will be changing this stage. When using 32 Ohm type of headphones, I would suggest you do comparative listening tests on as many different sets as you can. They are not all created equal and some can sound quite awful The Line Output: The line output circuit is also connected to the selector switch, but not to the level control. In other words, adjustment of the level control does not alter the output level of the line output. However, in common with the headphone amplifier, it is dependant on the setting of the selector switch. Thus if the selector switch is set to position 2, the line output will be the band pass filter output. The purpose of the line output is to provide a secondary audio output of fixed level that can be used to connect to an external recording device, a PC sound card or external amplifier. It cannot be used for driving low impedances such as headphones or earphones. As it has no gain adjustment control to affect it, it will always give the same output level for a given input level i.e. repeatability for external recording will make subsequent analysis more meaningful. Copyright P. Zimmermann 2010 Page 12

13 5.0. Operating Instructions: 5.1. Position the Microphone: This may seem rather obvious but the first step is rather important and so is worth spelling out. As the microphone is our window into the acoustic world of the bee, it is important to position the microphone within the hive in a realistic and practical manner. This needs a bit of thought as it needs to be done in a consistent and repeatable manner so that we can go back and repeat measurements or make comparisons at a later stage or perhaps with a different hive. This cannot be emphasized enough if we do not place the microphone in the same position, we cannot be sure we are making the same measurements or comparisons each time. That said, the bees will move around and the colony will expand / contract over the season/s. So it is up to the bee keeper to assess where the microphone is best located and whether it needs moving to suit the conditions within the hive There is no hard and fast guaranteed correct position within a hive but the microphone has been designed to be small enough to make locating it relatively straight forward. Ideally the microphone once positioned should be left in place such that the cable plug can be accessed externally and the Apimonitor connected without disturbing the hive. This won t always be possible and will obviously require the use of more than one microphone. Ideally each hive to be monitored would have its own microphone or alternatively if the microphone could be inserted or removed easily through a removable plug, then the microphone could be used as a measurement probe and inserted as and when required. Again bear in mind the repeatability of measurement The microphone is most sensitive on its end face and ideally the end face should face the source of the sound being measured. This isn t easy in a hive. Where is the source of the sounds we are trying to measure? My assumption is that we need to be monitoring the centre of the brood nest / chamber as this is where the queen is normally to be found but there may be better locations. Time will tell The microphone should be located as close to the sound source as possible. This will maximize the loudness of the sounds to be measured and minimize the effects of any external / unwanted background noises If possible, the microphone should be located in a space between frames / combs where there is less likelihood of the bees taking exception to it and covering it with propolis. This is probably an impossible aim as bees will invariably trample over the microphone, which in itself will generate noise in the microphone signal. Any foreign object placed in a hive will generally receive the bees full attention and eventually a good coating of propolis will ensue. Only time and experience will determine how quickly propolis will build up and where in the hive is to be found the best or optimum position for the microphone. Copyright P. Zimmermann 2010 Page 13

14 5.6. I would recommend the fitting of an additional screen or mesh to the microphone front face so that if propolis is a real problem the additional screen or mesh can be easily removed and cleaned. A mesh size of 3mm or smaller should be adequate. Alternatively the whole microphone could be mounted in or under a mesh cover perhaps. See section General Monitoring: Assuming the microphone is now correctly located within the hive, connect a pair of 32 ohm headphones and turn on the Apimonitor, set the selector switch to position 1 (All Pass) and increase the volume / level control until something is audible. Depending on the level of the sounds heard, the LED may be seen to illuminate. If nothing can be heard or very distorted sounds are heard then try changing the battery. Switch position 1 will pass most sounds that the bees make that we are likely to find audible. So, all being well you will be able to hear everyday bee activity. Note: The headphone socket is wired for mono sound although you will hear it in both ears it is not true stereo sound To concentrate on the warbling sound that is generally associated with swarming behaviour, set the selector switch to position 2 (Band Pass). This will apply a narrow filter to the sounds picked up by the microphone and reduce the level of other unwanted sounds. The centre frequency of the Band Pass filter is around 250Hz and dependant on the level of the warbling activity, the brighter the LED will glow as the volume or level control is advanced. Note: When listening to this switch position it will sound muffled / bassy and this is entirely normal. It is due to the attenuation of frequencies outside of the filter response. In order to make a comparison of the warbling activity on a day to day basis, let s say that on day 1 the LED just starts to glow with a volume or level setting of 8. Without changing the microphone location etc, on day 2 we repeat the measurement and find the LED starts glowing with a volume or level setting of 5. That means the level of warbling has increased because we have to turn down the level or volume control to get the same brightness at the LED. In other words, the louder the warbling, the lower the setting of the level / volume control for the same brightness. This may seem a bit confusing and possibly counter intuitive but think about it If there was very little in the way of warbling i.e. a very quiet hive, then you would have to turn the level / volume control up much higher in order to hear anything and therefore it would be a higher setting before the LED glows if at all. With practice the beekeeper will get a feel for what setting of the level / volume control equates to what bee activity is being observed. This is a most important point and is the reason why Eddie Woods spent so many years studying bee behaviour whilst at the same time making many sound measurements The level detector and LED indicator have been optimized for use with the band pass function but will however work on the other two switch settings. The High Pass setting though, will be less sensitive. Switch setting 3 or the High Pass setting applies a rising response filter to the microphone signal and is optimized to listen to the hissing sound bees make if the side of the hive is tapped. The sounds heard through the headphones in the High Pass switch Copyright P. Zimmermann 2010 Page 14

15 position will sound very thin and tinny and are entirely normal and due to the lower frequencies being heavily attenuated. As a check you can try high frequency sounds in front of the microphone try saying Yes into the microphone whilst emphasizing the ess. Alternatively jangle a bunch of keys near to the microphone and you will find it very sensitive to the high frequencies produced Recording / Long Term Monitoring: There may be times when you need to monitor the hive over a longer period and maybe unattended. You may want to record to a tape recorder, solid state recorder or to a computer in order to analyse the sounds at your leisure, either way make sure you use a fresh battery for long term recording. This is straight forward to do and all that is required is to connect the line output to the line input of your chosen recording device. Be certain to use a good quality screened lead. Temporarily connect your headphones to the headphone socket, switch on the Apimonitor and increase the level / volume control until you can hear hive activity. Once you are happy that all is well, make sure the selector switch is set appropriately (see below), leave the Apimonitor switched on, reduce the level / volume control to minimum and unplug the headphones. This will minimize the battery drain. Without the headphones and LED operational, a theoretical battery life of around 100 hours should be possible but this will be heavily dependant on the type of battery used. If leaving the Apimonitor unattended at the hive, do make sure that it is protected from the elements and is not likely to be chewed or trampled by beasties or children. The switch position will determine the signal present at the line output. So if you are going to apply filtering to your recording by say using a PC and suitable software, then set the selector switch to position 1, the All Pass function. All frequencies picked up by the microphone will then be present in the recorded data. If you want the recorded data to be pre-filtered then use the Band Pass or High Pass switch positions as required. Note: Line output levels are typically in the 100 mv region and are thus too high to connect directly to a microphone input. If all you have is a microphone input, then you will need to attenuate the signal from the line output. The line output uses a standard stereo output socket but both channels are wired to the same source i.e. the output is 2 channel mono sound. Copyright P. Zimmermann 2010 Page 15

16 6.0. Maintenance. 6.1 The Microphone The microphone is probably the single most important part of the Apimonitor. It consists of 3 main parts: a. The electret microphone capsule b. The connecting cable c. Connecting plug. The microphone capsule is a small 6mm diameter electret element which is mounted inside a small brass tube which affords additional mechanical protection and provides electrical screening to prevent pickup of electrical noise. A resilient sleeve covers the outside of the microphone body and also retains a small protective mesh disc to protect the front face of the microphone. The microphone construction has been deliberately kept simple to minimize cost and to facilitate mounting in confined spaces. If you are using a separate mesh enclosure for the microphone, the resilient outer sleeve and mesh disc can be removed. The connecting cable is a small diameter screened cable which connects the electret element to the plug. The cable screen is electrically connected to the brass tube to ensure a complete electrical screen is maintained between the electret element and the cable plug. The 3.5mm plug is a standard mono audio type plug and is used to connect the microphone to the Apimonitor. Other types of pc / media type electrets can also be connected if they are wired in the same manner, although they may give very different results. (Tip = signal / power +ve, Outer = Gnd) The microphone is essentially maintenance free but the following points should be observed: Keep the microphone dry and avoid contact with fluids. Water ingress will be certain death for the microphone. Keep the microphone clean and free from dust. If necessary wipe the microphone, cable and connector with a damp cloth and allow to dry naturally. Do not disconnect the plug by pulling on the cable. Keep the cable away from sharp edges / objects and avoid crushing the cable. During use and due to its location within the hive, it is likely that the front face of the microphone will become contaminated with propolis. This will rapidly degrade the performance of the microphone and will need to be removed. Wipe as much off of the outer microphone surface as possible, then gently prize the protective mesh from the front of the microphone. The outer sleeve is resilient and the mesh can be gently eased out. Take great care not to poke or prod the front face of the microphone with sharp implements. The mesh can then be gently cleaned in alcohol or acetone. When dry carefully replace the mesh back on the front of the microphone. If propolis proves to be problematic then fit a secondary mesh to avoid Copyright P. Zimmermann 2010 Page 16

17 contamination of the microphone mesh and to facilitate cleaning. In any event it is recommended to fit a secondary mesh to afford the microphone greater protection. It doesn t actually need to be a mesh. Any structure that has gaps small enough to prevent bees accessing the internal face will do. So a short tube placed over the microphone, drilled around its periphery and end face with say 3mm holes, would probably suffice. Note: This will however modify the directional characteristics of the microphone. Do not place the microphone in the hive without the protective mesh. If propolis gets inside the microphone, it will be impossible to remove Battery: The recommended battery is a standard alkaline 9 volt PP3 (MN1604 / 6LR61) readily available from many sources. It is a non-rechargeable type and the use of rechargeable variants is not recommended. The battery should yield approx. 40 to 100 Hours of use but this will depend on the operating durations / temperatures etc. If the operation of the Apimonitor is suspect, replace the battery as a matter of course. Always turn the Apimonitor off when not in use. If storing the Apimonitor for extended periods always remove the battery. Dispose of old used batteries in a responsible manner The Main Apimonitor Box: Apart from keeping the main unit clean with a damp cloth, little else is needed in the way of maintenance. Keep the unit dry and do not immerse. Avoid drops and sudden shocks. Avoid extremes of temperature. Only use the battery type recommended. Copyright P. Zimmermann 2010 Page 17

18 6.4. Testing: The Apimonitor is a relatively simple and rugged unit and as such should give reliable service. However, if for some reason you are not sure if it is working correctly, then there are a few simple checks that can be carried out. Check the obvious first. If the unit appears to be completely dead, always try replacing the battery in the first instance. If the unit emits a continuous whistle, turn down the level control and gradually increase it to the required level. If the whistle continues, replace the battery. To check the microphone make sure it is plugged in to the Apimonitor microphone socket. Plug in your headphones and switch the Apimonitor on. Set the selector switch to position 1 (All Pass) and if you can hear sounds picked up by the microphone then all is well. If you speak loudly into the microphone and gradually increase the level / volume control, the LED should be seen to flash in sympathy with peaks in the sound level. If you hear loud crackling when the microphone and / or cable are moved then you have a faulty / damaged microphone cable. Replace the microphone. Similarly if you hear pronounced humming if you handle or place your hand near the microphone, then the cable screen is faulty. Replace the microphone. If you hear nothing at all, then try an alternative microphone. Assuming the microphone is working, the switch filter positions can be checked in turn. With microphone and headphones connected, set the selector switch to position 1 (All Pass). Switch the Apimonitor on and position the microphone in front of a natural sound source such as a FM radio or CD player for example. Place the microphone directly in front of and facing the loudspeaker of the sound source. Turn up the level / volume control until the audio can be clearly heard. It should sound natural with no significantly enhanced or reduced frequencies. If it sounds dull or muffled, check the microphone mesh is clean and clear of debris. Set the selector switch to position 2 and now the audio heard in the headphones should appear distinctly different. This is the Band Pass position and will sound somewhat muffled with plenty of bass. Any musicians among you can check the filter response by using the appropriate note (B3 I think) the microphone should be quite sensitive to this note and the LED will light dependant on the setting of the level / volume control. Set the selector switch to position 3 (High Pass). The audio will now appear thin and tinny. This is correct and if a set of keys is jiggled in front of the microphone, a strong response to the high frequencies will be heard. The LED will respond to the higher levels dependant on the setting of the level control. Copyright P. Zimmermann 2010 Page 18

19 7.0. Notes For The Experimenter: This design has been presented as a starting point for anyone interested in taking the research of bee / hive acoustics further. It is not and never was intended to be a complete answer to all things acoustic and due to its simplicity and low cost some features have either been compromised or left out. This is the great engineering compromise where cost, simplicity, usefulness and market all have their impact. No two engineers will give you the same answer to this conundrum. So where can this design be taken from here? Well how long is a piece of string? There are many paths that lead off in different directions from here and it very much depends on what the reader sees as priority when viewed in the context of his own personal interest. The following discussion will expand this in a bit more detail but is by no means an exhaustive analysis on the subject Application: Although the Apimonitor has been targeted at the bee keeper, this unit could form the basis of many other acoustic monitors, albeit with a bit of tweaking in places. There have been suggestions of monitoring a bee hive with a vibration transducer to see what mechanical sounds the bees produce when stomping around the hive. The present filters within the Apimonitor could be tweaked or replaced in many ways to yield tuneable filters that can be adjusted to suit the frequencies of interest or very narrow filters to look at very specific frequencies. With the appropriate microphone, birdsong and other insect sounds could be monitored. Replace the microphone with a suitable transducer and listen to the mechanical sounds from say a car engine or the woodworm in your floorboards. Connect it to a hydrophone and listen to the sounds produced by fish and yes they do make noises. I m sure there are many other applications that I haven t even thought of so over to you for the ideas. What is obvious though and Eddie Woods realized all too well, is that it is all very well measuring and recording the sounds made by different animals / insects but without detailed observation it all becomes meaningless The Microphone: For an acoustic monitor this is a key item and in order to make recordings where a wide range of frequencies are going to be present, a flat response is desirable. In the appendix the frequency response of the microphone used with the Apimonitor is shown and this is nicely flat across the range of frequencies of interest. There are a multitude of different microphones on the market embracing various technologies, and all coming in different shapes and sizes. Their output characteristics and sensitivities vary widely so be careful what you choose and study the manufacturer s data carefully. The electret microphone is probably ideally suited to the Apimonitor application, but even that could be optimized further for sensitivity, noise cancelling, physical size etc. In recent years, silicon microphones have become available and by use of micro machining technology are now extremely small and quite cheap. They are not generally sealed though, so you need to make sure they are protected from dust, the elements etc. For airborne noises microphones are ideal. For sound transmitted in other mediums, different transducers will be required. For vibration in a mechanical structure, vibration sensors or accelerometers will be appropriate. For water a hydrophone or pressure transducer are the more usual sensors. Copyright P. Zimmermann 2010 Page 19

20 8.0. Appendix: Apimonitor Ver Filter Responses - Measured at Line Output -20 O/P dbv Hi Pass Band Pass All Pass Frequency (Hz) Fig 1 Measured Filter Responses Apimonitor Ver Band Pass Filter Response - Electrical - I/P -60 dbv O/P dbv -20 Band Pass Hz Frequency (Hz) Fig 2 Magnified Band Pass Filter Response Copyright P. Zimmermann 2010 Page 20

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